He organized the theatre company Ninchi-Dori-Tumiati and founded the avant-garde group Palcoscenico (Stage).

[1] During the Second World War, he was conscripted into the army but went over to the Italian resistance movement, including working with the socialist newspaper Avanti!.

In 1947, with Giorgio Strehler, friend and associate,[2] Grassi founded the Piccolo Teatro di Milano, the first Italian civic theatre.

[4] From 1972 to 1977 he was superintendent of the La Scala theatre, while from 1977 to 1980 held the post of president of Italy's state broadcaster RAI.

Grassi died in London in 1981 following heart surgery and is buried at the Monumental Cemetery of Milan.